This invention relates in general to electrically driven timers and in particular to an expanded scale timer and a method of operating such.
In the past, various and sundry types of expanded scale or dual speed timers have been utilized in laboratories, factories, and homes for controlling the operating time or cycle of devices requiring rather accurate time measurements for relatively short periods of time but also having timing cycles which may extend over relatively longer periods of time. For instance, one of the more prevalent uses for expanded scale timers is in conjunction with various home appliances, such as an oven or the like. Many of the modern day foods may require only a short period of time for cooking, e.g. about five or ten minutes; therefore, it is necessary to accurately time the cooking period for such foods in order to obviate over-cooking or perhaps burning them. Further, at least some of the modern day ovens, such as an induction type cooking unit or mechanical vibration type cooking unit as well known in the art, are operable to prepare or cook foods in a relatively short period of time as compared with a conventional oven; therefore, it is necessary to accurately time the cooking or operating cycle of such modern day ovens over such relatively short period of time in order to prevent over-cooking or perhaps burning of some foods. Quite obviously, it is also desirable to provide a longer cooking cycle or operating time period for both the conventional type oven and the modern day induction and mechanical vibration type ovens. In order to achieve such accurate regulation or timing during relatively short time periods, the timing scale for the past timers has been elongated or expanded for the relatively short time periods, i.e., from zero to five or ten minutes, so that the desired time setting for any particular operating or timing cycle may be more accurately achieved within the elongated or expanded setting ranges for the shorter periods of time. For instance, in a dial having angularly spaced dial settings from 0.degree. to 360.degree., the expanded time settings for the relatively short time period of five minutes may occupy the first 165.degree. to 180.degree. of the 360.degree. dial settings, and the successive relatively long time period, i.e., from about thirty minutes to several hours, may occupy the following 165.degree. to 180.degree. of the 360.degree. dial settings. Of course, in order to compensate for the above-discussed expanded time scale for the relatively short period of time, the past timers were operated at a relatively high speed during the short time period in the elongate scale and at a lower speed during the long time period.
In some of the past expanded scale timers in order to attain the high and low speed or dual speed operation thereof, separate motive force applying or motor pinions were driven by separate electric motors, and these motor pinions were clutched together by a cam operated shift arm engaging or disengaging between the motor pinions in overriding relation to effect the dual speed operation. Of course, it is believed that a disadvantageous or undesirable feature of this particular type of past expanded scale timer was not only the expense of providing separate motors for operating it but also the complexity of regulating or clutching them to attain the dual speed operation.
In some other types of past expanded scale timers, two sector-shaped gears of different diameters were conjointly driven and had their respective teeth portions off-set with respect to each other thereby to engage successively with two mating pinion gears also of different diameters in order to effect dual speed operation of such past expanded scale timer. One of the disadvantageous features of this type of past expanded scale timer is believed to be the problem of angularly positioning the sector-shaped gears, i.e., accurately spacing the sector-shaped gears from each other in order to achieve successive and uninterrupted meshing of their respective teeth portions with the associated pinion gearing. In an attempt to overcome this disadvantageous feature, the adjacent ends of the sector-shaped gears were overlapped; however, it is believed that in itself created another disadvantageous feature in that each time the timer translated from the low speed to the high speed operation thereof, the gearing could be mismeshed or be in interferring engagement. Even though it may be possible to overcome or properly design around this gearing interferring engagement or disadvantageous feature, it may require the development of special gearing which in itself may disadvantageously add to the complexity as well as the cost of this type of expanded scale timer.
In still another type of past expanded scale timer, a low speed pinion and a high speed pinion were driven by an electric motor, and a time interval gear mounted on the time set shaft was axially movable both manually and automatically into and out of engagement with the low and high speed pinions thereby to effect the low and high speed modes of operation. A latch cam was operative to axially move the set shaft so that the time interval gear was automatically axially moved therewith toward engagement with the high speed pinion. It is believed that at least one of the disadvantageous or undesirable features of this type of past expanded scale timer involved the improbability of properly meshing the teeth of the pinion gears with that of the time interval gear as it was axially moved toward the pinion gears, and of course, it is believed that this attempt at moving the gearing axially to effect meshing thereof may also be accompanied by a back-lash problem which also may have a disadvantageous effect on the gearing as well as the shafts to which such gearing is mounted.
In yet another of the past expanded scale timers, a segmented time interval gear was rotatable in driven relation between a low speed pinion and a high speed pinion to effect the dual operating modes of the timer. While this type of past expanded scale timer may have been desirable as compared with others of the past timers, it is believed that there was present the problem of a driving gap between the disengagement of the time interval gear from the low speed pinion and the engagement of the time interval gear with the high speed pinion which may be viewed in some respects as a disadvantageous or undesirable feature. Further, it is believed that the transition between the low and high speed modes of operation may also have resulted in a back-lash problem which, of course, may also be disadvantageous.
Many other types of past expanded scale timers too numerous to discuss in detail utilized driving pawls, ratchet arrangements, stop pins, cam drivers as well as many other arrangements to effect dual speed operation but each is believed to be accompanied by various disadvantageous or undesirable features attendent to such arrangements.